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Acoustic Vaporization Threshold of Lipid Coated Perfluoropentane Droplets Open Access

Ultrasound has been embraced as a non-invasive, well-understood and relatively inexpensive tool for diagnostic and therapeutic purposes compared to other imaging modalities such as computed tomography, positron emission tomography and magnetic resonance imaging. However, this modality suffers from low sensitivity. To overcome this limitation, ultrasound contrast agents have been introduced which are gas-filled colloidal particles with a size range of 1-7 micrometers. These microbubbles are highly echogenic and therefore they enhance the sensitivity of conventional ultrasound imaging by expansion and contraction in the alternating pressure waves of the ultrasound beam, while tissue is almost incompressible. Currently available microbubbles used for ultrasound imaging and therapeutics are restricted to intravascular space due to their micron size distribution. Recently an interest is developed in designing novel contrast agents with enhanced stability in vivo and a sufficiently small size distribution for extravascular interrogations (Fig.1). Introducing phase-shift droplets which consist of a nanoscale droplet of perfluorocarbons in an encapsulating shell has led to novel ways of approaching ultrasound-based techniques for both diagnostic and therapeutic purposes. These droplets undergo a phase transition to the highly echogenic gaseous state and are convertible to micron-sized bubbles upon the input of sufficient acoustic activation energy which is termed as acoustic droplet vaporization (ADV) [1]-[3]. In this study, we investigated the ADV thresholds and its dependence on excitation pressure and frequency using acoustic recordings. In addition, we have also compared the scattered response from droplets with that of conventional microbubbles at the corresponding excitation pressure and frequency.

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